Magnetic interactions, anisotropies and electrical properties present in ferromagnetic nanotubes of manganites.

J.CURIALE; R. D. SANCHEZ; M. GRANADA; H. E. TROIANI; M.I. DOLZ; H. PASTORIZA; A.G. LEYVA; P. LEVY

Rio de Janeiro Brasil

Conferencia; Nano 2008, 9thInternacional Conference on Nanostructured Materials.; 2008

Ferromagnetic (FM) manganites, La0,67Sr0,33MnO3 (LSMO) and La0,67Ca0,33MnO3 (LCMO), have been extensively studied in the last decade due to the colossal magnetoresistance phenomenon. In particular we present results about these FM manganites with tubular morphology at the nanoscale. Their FM transition temperatures (TC) in bulk are 360 K and 270 K for LSMO and LCMO, respectively. Although small changes in TC are observed in the nanotubes, the rest of their magnetic properties are notably affected. The external diameters are varied between 800 and 200 nm. The walls are constituted by an assembly of nanoparticles, with size approximately between 25 and 30 nm. The wall thicknesses are 45 nm for LSMO and 60 nm for LCMO. Our previous study [1] shows that each grain is a single magnetic domain, with a thick dead layer on the surface, and the magnetic interactions between them are essentially of dipolar character. In order to characterize completely the interactions between the magnetic nanograins, we present a study of First-Order Reversal Curves (FORC) diagrams. Also, we complement the FORC results with delta M curves obtained from the isothermal remanent magnetization (IRM) and the DC demagnetization (DCD). We discuss the role of the interaction in the configuration of the magnetic moments in these nanostructures. We complete this study with the results of Ferromagnetic Resonance technique on aligned LSMO nanotubes about the magnetic anisotropies present in the nanotubes. [1] J. Curiale, R. D. Sanchez, H. E. Troiani, H. Pastoriza, C. A. Ramos, A. G. Leyva  and P. Levy.  Phys. Rev. B 75, 224410 (2007)